US Marines engaged in a fierce battle with insurgents which left at least 21 suspected Taliban dead, as violence continues in the former strongholds of the fundamentalist militia, officials said Wednesday.

"In excess of 20 anti-coalition militants were killed" and one detained in the US-led offensive in south-central Afghanistan on Tuesday, US military spokesman Lieutenant Colonel Tucker Mansager told a press conference in Kabul.

Two US marines, two Afghan soldiers and an Afghan interpreter were wounded in the action near the US base in the southcentral province of Uruzgan but all were in a stable condition, he said.

"Marines... continued their assault into the Taliban heartland where they killed more Taliban fighters who were poised to ambush the marines in central Afghanistan," the US military said in a statement released late Tuesday. An Afghan official said that American and Afghan forces had killed some 21 militants in fighting on the ground supported by US warplanes.

"We have 21 dead only yesterday (Tuesday)," Kandahar military spokesman General Abdul Wasay told AFP. "But 30 have been killed and about 10 injured in the past several days."

"There is a huge clean-up operation going on in the mountainous areas between Kandahar, Zabul and Uruzgan," he added.

Zabul security commander Mohammed Ayob confirmed the major operation which was going on in Uruzgan and in the border regions and the mountainous valleys of Deh Chopan in Zabul. "A joint Afghan and coalition operation, which was launched three days ago, is ongoing -- but there is no resistance right now," he told AFP.

"During this operation we believe that some 23 to 30 Taliban have been killed," he said, adding coalition aircraft had bombed the area. Uruzgan, Zabul and the southern province of Kandahar are adjacent to each other and the point at which they meet has been described by the US military as the "Taliban heartland" and is believed to host a permanent presence of fighters loyal to the ousted fundamentalist militia.

"We are having a great deal of success in our offensive operations down there in that area," Mansager said, adding that until recently the coalition did not have a significant presence there.

It is the arrival of some 2,200 marines in Uruzgan which has contributed to the heightened insurgent activity, he said. Mansager confirmed that sporadic violence continued around the country, following a bloody weekend when dozens of militants were killed in fighting in Zabul.

The latest fighting is the bloodiest since late last summer when hundreds of people, mostly Taliban fighters, were killed in Afghan and US-led offensives against militants in Zabul. Since then, militants have refused to gather in large numbers, preferring to launch guerrilla-style attacks on small numbers of Afghan and foreign soldiers or unarmed humanitarian and civilian workers.

Afghan officials believe some 500 to 800 Taliban fighters are holed up in Zabul's Deh Chopan district, some 300 km southwest of Kabul.

Intelligence and military officials told AFP that the insurgents were loyal to one of the ousted Taliban's leaders, Mullah Dadullah, a close lieutenant of the movement's fugitive founder, Mullah Mohammed Omar.

The past week has seen daily clashes between the US-led coalition force and militants with at least 25 insurgents dying in two days of fighting with marines in Zabul. Some 20,000 US-led mainly American coalition forces are in Afghanistan to hunt and kill Taliban, Al-Qaeda and other militants.